Question

Which of the following is not correct for a gas undergoing isothermal expansion?

• A. $\Delta U=0$
• B. $\Delta T=0$
• C. $W=0$
• D. $\Delta H=0$

Answer 1

The correct option is C $W=0$

• $\text{For isothermal process}$, $\Delta T=0$
  $\text{we know}$
• $\text{At constant volume,}$ $q_v=C_v\Delta T=\Delta U$
  $\text{If}\Delta T=0$
  $\Delta U=0$
• $\Delta H=\Delta U+\Delta \left(PV\right)=\Delta U+nR\Delta T=0$
• $\text{Now from first law of thermodynamics}$$\Delta U=q+W$
  $\text{If}\Delta T=0\text{then}\Delta U=0\text{and}W=-q$
  $\text{Hence}W\ne 0$